Automatic compensation for inaccuracies in quadrature mixers

In an ideal software defined radio (SDR), all parameters are defined in software, which
means the radio can be reconfigured to handle any communications standard. A major
technical challenge that needs to be overcome before this SDR can be realised, is the
design of an RF front end that can convert any digital signal to an analogue signal at any
carrier frequency and vice versa. Quadrature mixing (QM) can be used to implement and
analogue front end, that performs up and down conversion between the complex
baseband centred around 0 Hz and the carrier frequency. By separating the tasks of
frequency conversion and digital-to-analogue conversion, the latter can be performed at a
much lower sample rate, greatly reducing the demands on the hardware. Furthermore, as
QM can handle variable carrier frequency and signal bandwidth, this can be done without
sacrificing reconfigurability. Using QM as an analogue front end may therefore be the
solution to implementing SDR handsets.